Developing apparatus having light transmitting window

Abstract: A developing apparatus includes a developer container (25) for containing a developer; a light transmitting portion (26a,26b), in the developer container, for optically detecting the developer; a rotatable wiping sheet (28) for wiping the light transmitting portion (26a,26b); wherein the wiping sheet (28) has a low rigidity portion at a rotational axis side beyond an end of the wiping sheet.

Description: FIELD OF THE INVENTION AND RELATED ART The present invention relates to a developing apparatus for developing an electrostatic latent image on an image bearing member usable with an image forming apparatus such as an electrophotographic apparatus, electrostatic recording apparatus or the like, as defined in the preamble of claim 1. It is conventional that a beam is introduced into a developer container for containing a developer, and the light transmitted through the container is detected to detect the presence or absence of the developer therein. Referring first to Figures 21 and 22, there is shown an example of such an apparatus. Figure 21 shows a light transmitting type, wherein reference numerals 115 and 116 designate a light emitting element and light receiving element, respectively. A developer container 125 is provided with a transparent window 126a and a transparent window 126b for transmitting the light at the position corresponding to light emitting element 115 and light receiving element 116. When a sufficient amount of the developer is in the developer container 125, the light from the light emitting element 115 having entered the developer container 125 through transparent window 126a, is blocked by the developer therein, so that the light will not reach the light receiving element 116. When the developer container becomes empty by the consumption of the developer, the light from the light emitting element 115 reaches the light receiving element 116 through the transparent window 126a and transparent window 126b. In this manner, the presence or absence of the developer is detected on the basis of the change of the output of the light receiving element 116. Figure 22 is an enlarged view of a cleaning member 129 for cleaning the windows. It is rotatable about shaft 129a by an unshown driving source. A cleaning blade 128 of flexible material is mounted to a tip end of the cleaning member 129 and is brought into contact with the inside surfaces of the transparent window 126a and transparent window 126b and wipes the developer T thereon out, with rotation of the cleaning member 129. By doing so, it is avoided that the erroneous discrimination of presence of the developer due to the contamination of the windows, despite the absence of the developer. Patent Abstracts of Japan, vol. 14, no. 124 (P-1018); & JP-A-1 319 065 discloses such a developing apparatus comprising a wiping sheet fixed to a rotatable cleaning member. As one of factors influential to the cleaning of the windows, there is a contact angle  between the cleaning blade 128 and the window surface. If the contact angle is small, the angle of the force applied to the window surface is close to 90 degrees, as as shown in Figure 23, (a), the cleaning blade 128 presses the toner particles to the window surface and ride over them, with the result that the toner remains on the window surface, and therefore, the cleaning effect is not so strong. So, the contact angle is preferably 90 degrees. However, if the contact angle is very close to 90 degrees, the blade does not reach to the window surface, if it is even slightly shorter than required with the result of the liability of incapability of the cleaning. The result is that the positioning between the window surface and the blade is highly accurate. This increases a manufacturing cost of the apparatus. Additionally, if the contact angle is very close to 90 degrees, and if the blade is deformed even slightly by the resistance caused by the scraping action, the cleaning of the window becomes not possible. Therefore, it is required that the sufficient entrance amount d of the blade and the contact angle are determined in consideration of the positional accuracy and the deformation of the apparatus. On the other hand, the recent demand is directed to downsizing of the developing apparatus. To meet this, a flat developing apparatus is proposed from the standpoint of the space saving or for a small size cartridge. When the size of the developing apparatus is reduced, the entrance amount of the blade d has to be reduced, with the result of the following problems. In order to provide the sufficient cleaning effects, d>0 is required even if the d is small, and therefore, the positional precision is required, which leads to the increase of the cost. If the entrance amount is too large, the contact angle becomes small, the cleaning effects are deteriorated. Furthermore, when the deformation of the blade increases, the difference in the torque required when the blade is cleaning the window surface and that when the blade is out of contact to the window surface increases. This increases the variation of the torque during the image forming operation with the possible result of the deterioration of the quality of the resultant image. SUMMARY OF THE INVENTION Accordingly, it is a principal object of the present invention to provide a developing apparatus wherein a transparent window can be effectively cleaned. It is another object of the present invention to provide a developing apparatus wherein the difference of the driving torque between when the cleaning blade is in the cleaning operation and not in the cleaning operation is reduced. These objects are solved by a developing apparatus and an image forming apparatus as defined in claim 1 and 5 respectively. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention takcn in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of an image forming apparatus according to an embodiment of the present invention. Figure 2 is a longitudinal sectional view of an image forming apparatus of embodiment 1. Figure 3 illustrates an operation of mounting and demounting a process cartridge relative to the image forming apparatus of embodiment 1. Figure 4 is a front view of a cleaning member used in the apparatus of embodiment 1. Figure 5 is a longitudinal sectional view of a process cartridge according to embodiment 1. Figure 6 is a perspective view of a major portion of a process cartridge according to embodiment 1. Figure 7 illustrates modified example of the cleaning blade in embodiment 1. Figure 8 shows a cleaning blade used in embodiment 1. Figure 9 schematically shows a relationship between the contact angle of the cleaning blade to the transparent window and the position of the low rigidity portion of the cleaning blade in embodiment 1. Figure 10 shows a relationship among stirring blades, transparent window and the cleaning blade in embodiment 1. Figure 11 schematically shows an output signal of a light receiving element in embodiment 1. Figure 12 shows a cleaning member in embodiment 2. Figure 13 shows a cleaning member in embodiment 3. Figure 14 shows a cleaning member in embodiment 4. Figure 15 shows a cleaning member in embodiment 5 (not covered by the present invention). Figure 16 shows a cleaning member in embodiment 6. Figure 17 is a longitudinal sectional view of a process cartridge in embodiment 6. Figure 18 is a longitudinal sectional view of a process cartridge in embodiment 6. Figure 19 is a longitudinal sectional view of a process cartridge in embodiment 7. Figure 20 is a perspective view of stirring blades in embodiment 7. Figure 21 is a longitudinal sectional view of a process cartridge. Figure 22 is a perspective view of stirring blades used in Figure 21 structure. Figure 23 shows a relationship between the contact angle of the cleaning blade and the wiping force for the developer. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figures 1-11, an embodiment of the present invention will be described. The exemplary image forming apparatus taken in the embodiment is an electrophotographic type facsimile machine. In Figures 1 and 2, a top cover of the main assembly of the apparatus 1 is constructed to permit to place a stack of original documents thereon. Adjacent one end of the top surface (left-hand side in Figure 2), an optical reader 3 for reading image information of an original fed from the original platen 2, above the reader 3, an operation panel 18 is provided. Below the reader 3, a recording system comprising a laser beam printer is located. The optical reader 3 separates one by one the originals D on the original platen 2 by a prefeeding roller 5b press-contacted to a prefeeding pressing member 5a and a separation roller 5d press-contacted to a reversing roller 5c, and feeds it to a contact sensor by original feeding roller pair 5e or the like. The image information of the original D is read while an urging means presses the original D onto the contact sensor 7, and thereafter, the original D is discharged to the discharge tray 8 by discharging pair of rollers 5f. The contact sensor 7 emits light to the image information of the originals from LED 7a functioning as a light source, and the light reflected thereby is imaged on a photo-electric converter 7c through a short focus imaging lens 7b. The read information is transmitted to a recording station of another machine in a facsimile mode and is transmitted to a recording system of itself in a copy mode. Original platen 2 is provided with a slider 2a slidable in a direction perpendicular to a feeding direction of an original (width direction of the original D). The slider 2 is operated to meet the width of the original to align the lateral edges of the originals. A laser beam oscillator 9a of the recording system 4 emits a laser beam modulated in accordance with the image signals of the contact sensor 7, and the modulated beam is deflected by a polygonal mirror 9b and is directed to a photosensitive drum 21 in an image forming station as image light. The image information is converted to an toner image, which in turn is transferred onto a recording sheet p', and fixed thereon. Then, the recording sheet p' is discharged. The photosensitive drum 21 is integrally contained in a process cartridge 20 together with a primary charger 22, a developing device 23, a cleaner 24 and a developer container 25 for containing a developer T, and the process cartridge is detachably mountable to the main assembly 1 of the apparatus. The image forming operation will be described. The surface of the photosensitive drum 21 (image bearing member) is uniformly changed by the primary charger 22, and is subjected to the image light L from the laser beam oscillator 9a, by which an electrostatic latent image is formed on the photosensitive drum 21. The electrostatic latent image is visualized into a toner image by the developer (toner T) supplied from the developing device 23. The toner image on the photosensitive drum 21 is transferred onto a recording sheet p' fed from a sheet feeder A, by a transfer charger 10 disposed adjacent to the photosensitive drum 21. The recording sheet p' now carrying the toner image is subjected to image fixing of an image fixing device 10g so that the toner image is fixed on the sheet. Then, the sheet is discharged discharging pair of rollers 11h to a discharge tray 12 detachably mounted to a sides of an apparatus (left side in Figures 2 and 3). On the other hand, the photosensitive drum 21 after the image transfer operation, is cleaned by the cleaner 24 so that the residual toner or the like is removed, thus preparing for the next image forming operation. On the original platen 2, there is an openable cover. When it is opened, process cartridge 20 can be removed and exchanged. The process cartridge 20 is provided with a shutter 30 for blocking it from the light. The shutter 30 automatically opens when the process cartridge is mounted in the apparatus, and the shutter 30 automatically closes when it is taken out of the apparatus. A light emitting element 15 is mounted on an inside surface of the top part, and a light receiving element 16 is mounted on the main assembly of the apparatus. They are so disposed that when the process cartridge 20 is mounted to the main assembly 1 and the cover 14 is closed, they are faced with the developer container 25 therebetween. The developer container 25 is provided with a transparent window 26a and a transparent window 26b interposed between the light emitting element 15 and light receiving element 16. The detecting light emitted by light emitting element 15 is directed into the developer container 25 through the transparent window 26a. When the developer container 25 contains a sufficient amount of the developer T, the light is blocked by the developer T. When the developer container 25 does not contain the developer T, the light passes through the transparant window 26b to the outside of developer container 25 to reach the light receiving element 16, so that the absence of the developer T can be detected. In the sheet feeding station A, a topmost one of the sheets stacked on a cassette 40 which is retractable from one side of the bottom portion of the apparatus, is fed out by cooperation of separation claws 41 at the front corners and a crescent pick-up roller 36. The sheet is then fed to a feeding roller as a pair of registration roller, by a pair of feeding rollers 38. The registration roller feeds the sheet, in timed relation with the leading edge of the toner image on the photosensitive drum 21, to the image transfer position formed by a transfer charger 10f and the photosensitive drum 21. Referring to Figures 4-11, the description will be made as to a developer detection device for detecting absence or presence of the developer. Figure 4 is a front view of a cleaning member according to an embodiment of the present invention. Figures 5 and 6 are longitudinal sectional view and a perspective view of a major part of the developer detector. The light emitting element 15 and light receiving element 16 are mounted on the main assembly 1 so that they are faced to each other. Designated by S is an optical axis connecting therebetween, and R is an optical path of the detecting light incident on the light receiving element 16. The transparent window 26a and transparant window 26b are formed in a top wall 25a and a bottom wall 25b of the developer container 25. Here, "transparent" means transparent relative to the light or beam emitted by the light emitting element 15, and does not necessarily means "visually transparent". A stirring blade 27 and a stirring arm 31 are provided in the developer container 25. A shaft 27a adjacent an end of the stirring blade 27 is engaged with a hole 31a of stirring arm 31. Stirring blade 27 has an opening 27b so as not to interfere with the optical path R, and ribs 27c provided with U-grooves are formed at both sides thereof. Stirring arm 31 is rotatably supported on a shaft 31b on a side of the developer container 25. An end thereof extends outwardly from the side of the developer container 25, and an end portion thereof is provided with an integral driving arm 31c. A a stirring gear 32 is mounted to the outside of developer container 25, and rotates about shaft 32a with the rotation of the photosensitive drum 21. A pin 32b is eccentric from the shaft 32a, and is engaged with a hole 31d of the driving arm 31c. When the a stirring gear 32 rotates with rotation of the photosensitive drum 21, the stirring arm 31 reciprocates in direction X about the shaft 31b. The stirring blade 27 reciprocates in direction Y along the bottom of the developer container 25 to feed the developer T into a developing chamber and to prevent agglomeration of the developer T or the non-uniform distribution of the developer T in the developer container 25. The bottom wall 25b of the developer container 25 is slanted toward the developing chamber to assist the supply of the developer T to the developing chamber. A cleaning member 29 is for cleaning the transparent window 26a and transparant window 26b, and is rotatably supported on shaft 29a. A driving shaft 29c is an eccentric driving shaft eccentric from the shaft 29a, and is engaged in the U-groove of the stirring blade 27. When the stirring blade 27 reciprocates in the direction Y, the driving shaft 29c receives force from a rib 27c, to reciprocally swing the cleaning member 29 about shaft 29a in a direction Z. The angle of the swinging motion is preferably less than 100 degree to permit smooth sliding between driving shaft 29c and rib 27c. A cleaning blade 28 is in the form of a wiping sheet of flexible material, and is fixed on the cleaning member 29 on substantially a central portion 28b of the cleaning blade 28, the opposite end portions are extended out through slits 29d formed in the end portions 29b of the cleaning member 29. An opening 28c is formed in the cleaning blade 28 so that the cleaning blade 28 continues to block the optical path R. By doing so, the optical path R is blocked only when the the end portion 29b and the cleaning blade 28 are in the center of the path R, despite the fact that the shaft 29a is disposed at a position blocking the optical axis. Therefore, the presence or absence of the developer T can be detected when the end portions 29b or the cleaning blade 28 blocks the optical path R. Figure 7 shows a comparison between a modification of the cleaning blade shown in Figure 21 and that of this embodiment. When the positional relations between the cleaning member and the transparent window are the same, the cleaning blade deforms significantly adjacent opening 28c as shown in Figure 7, (b) because of the provision of the opening 28c in the cleaning blade in this embodiment. The deformation in the other position is less. As a result, the entrance amount d required to provide the contact angle = 1 as in Figure 21 can be increased, that is, d2>d1. For this reason, even if the cleaning member 29 is made smaller for the purpose of downsizing the apparatus, the entrance amount d is not required to correspondingly reduced at the same proportional ratio, and positional accuracy is not required to be increased. By fixing cleaning blade 28 at the substantially central portion 28b of the cleaning blade, the length of the free portion of the cleaning blade can be increased as compared with the case wherein the downsizing is accomplished by mounting a short cleaning blade 128 on the end of the cleaning member 129. In addition, the opening 28c is effective to decrease the rigidity of the cleaning blade 28, and therefore, the rigidity of cleaning blade 28 can be reduced to maintain the low resistance against deformation of the cleaning blade 28. Because of this, there is no need of increasing the driving torque of the apparatus, and there is no liability of deteriorating the image quality. In addition, the integral structure of the two blades, the number of assembling step is decreased. The rigidity and the deforming portion of the cleaning blade 28 can be controlled relatively freely by changing the fixed length l 1, that is, by changing the free length l 2, or by changing the width w1 of the opening 28c, that is, the width w2 of the narrow portion of the cleaning blade. Alternatively, as shown in Figure 8, the opening 33c of the cleaning blade 33 may take such a configuration that the deformation of the cleaning blade is more concentrated. Thus, by changing the configuration of the opening of the cleaning blade, the contact pressure and the contact angle between the window surface and the cleaning blade can be determined to provide the satisfactory cleaning. Therefore, the design latitude for the entrance amount or the mounting position of the cleaning blade or another structure can be increased. Figure 9 illustrates relation among the position of the low rigidity portion of the cleaning blade, the free length N of the cleaning blade and the entrance amount d of the cleaning blade to the window surface. If it is assumed that the deformation of the cleaning blade occurs only at the low rigidity portion, the contact angle  is equal to the contact angle without the low rigidity portion (Figure 9, (a)), when the positional relation between the cleaning blade and the transparent window are the same and when the distance m from the end of the cleaning blade and the low rigidity portion satisfies: d(2m-d) (m-d) 2 = tan 2 N(2dm-d 2 ) 1/2 m(N-d) Therefore, the contact angle  can be increased (2 > 1) without changing the entrance amount d by making a distance M from the end of the cleaning blade to the low rigidity portion larger than the m satisfying the above equation. Additionally, when the contact angle equal to that without the provision of the low rigidity portion in the cleaning blade is to be obtained, the entrance amount d can be increased by making the distance M beyond m. Referring to Figure 10, the description will be made as to the relation among the light emitting element 15, light receiving element 16, transparent window 26a, transparant window 26b and cleaning member 29. As described in the foregoing, the light emitting element 15 and light receiving element 16 are mounted to the main assembly 1 so that they are faced to each other with the developer container 25 therebetween when the process cartridge 20 is mounted to the main assembly 1. The shaft 29a of the cleaning member is adjacent the optical axis S, preferably, across the optical axis S. The transparent window 26a and transparant window 26b are faced to the transparent window 26a and transparant window 26b, respectively, and the transparent window 26a and transparant window 26b are so positioned that they are contacted by the cleaning member moving along a circumference of a circle about the shaft 29a. Therefore, the angle formed between the window surface and the optical axis S is very close to 90 degrees. Thus, the sizes of the transparent window 26a and transparant window 26b can be minimized as compared with the slanted window surface relative to the optical axis S. This is effective to minimize the deterioration of the image quality and the deterioration o the photosensitive drum 21 and the developer T attributable to the astray light. Additionally, the optical path length through the material of the window is shorter than that in the case of the slanted window, and therefore, the loss of the light energy due to the absorption or the scattering or the like by the material of the window can be suppressed. The 90 degrees incidence of the light from the light emitting element 15 can suppress the loss of light energy due to the reflection of the light by the surface. This eliminates the necessity for the use of a light emitting element of high intensity and wide directivity or the use of high sensitivity light receiving element, thus reducing the cost of the apparatus. These advantages are most effective when the shaft 29a across the optical axis S so that window surfaces of the transparent window 26a and transparant window 26b are perpendicular to the optical axis S. A distance H between the top transparent window 26a and the shaft 29a of the cleaning member, a distance I between the top end 29b of the cleaning member and the shaft 29a and a distance J between the top end to the cleaning blade 28 and the shaft 29a, satisfy I<H<J, as shown in Figure 10. A distance H' between the bottom transparent window 26a and the shaft 29a of the cleaning member, a distance I' between the bottom end 29b of the cleaning member and the shaft 29a and a distance J' between the bottom end to the cleaning blade 28 and the shaft 29a, satisfy I'<H'<J', as shown in Figure 10. Therefore, by the swinging motion of the cleaning member 29, the cleaning blade 28 is contacted to the window surfaces of the transparent window 26a and transparant window 26b while it swings, to wipe the developer T off the window surfaces thereof. Since the window surfaces are in contact with a circle having a center at the cleaning member 29 at this time, the transparent window 26a and transparant window 26b can be cleaned uniformly. According to this embodiment, even if the cleaning member 29 is downsized for the purpose of downsizing the process cartridge 20 or of flattening the developer container 25, the contact angle can be maintained without reducing the entrance amount d at the same ratio. It is also possible to maintain the resistance against the deformation of the cleaning blade 28, and the cleaning of the transparent window can be effected without increasing the driving torque and without deteriorating the image quality. It is not necessary to handle a thin and small blade so that the assembling of the apparatus is easy, and the number of the blade mounting steps can be reduced, thus reducing the manufacturing cost. In the above-described image forming operation, cleaning member 29 rotates to that the cleaning blade 28 removes the developer T from the transparent window 26a and transparant window 26b. When the amount of the developer T is sufficient, the developer T covers the window surfaces immediately after the cleaning blade 28 removes the developer T from the transparent window 26a and transparant window 26b, and therefore, the light from the light emitting element 15 does not reach the light receiving element 16, or even if it reach the light receiving element 16, it is quickly re-blocked. If, however, the amount of the developer T decreases, the time required for the developer T to cover the transparent window 26a and transparant window 26b. When the developer T is used up, the the light reaches the light receiving element 16 except when the transparant window 26b and the cleaning blade 28 crosses the optical path R. Figure 11 shows the output signals from the light receiving element 16, wherein the coordinate represents the output and the abscissa represents the time. When the light from the light emitting element 15 reaches the light receiving element 16, the output of the light receiving element 16 increases. The output signal of the light receiving element 16 takes alternately a high level and low level (sew teeth). With a sufficient amount of developer T, the time period of the high level is short (a), but with a decreased amount of developer T, the time period thereof becomes long (b). The time period t for which the level is higher than a predetermined level V is detected, and the absence of the developer T is discriminated when the period t is longer than a predetermined period t'. As described in the foregoing, the cleaning blade of a flexible material is provided with an opening, so that the rigidity of the cleaning blade is maintained low, and simultaneously, the deformation of the cleaning blade is concentrated on a predetermined position, by which even if the size of the cleaning member is reduced, the contact angle of the cleaning blade can be made larger without reducing the entrance amount of the cleaning blade. Embodiment 2 Referring to Figure 12, the second embodiment of the present invention will be described. Figure 12 is a front view of the a cleaning member used in this embodiment. In this embodiment, the transparent window 51 is cleaned by a plurality of cleaning blades 51, and the cleaning blades 51 have at least one opening 51a. Designated by a reference numeral 50a is a rotational shaft for the cleaning member, and 50c is a driving shaft of the cleaning member. This embodiment is the same as the foregoing embodiment in the other respects. The cleaning member 50 is used in place of the cleaning member 29, by which the driving shaft 50c receives force from the rib 27c of the stirring blade 27 so that the cleaning member 50 swings about the rotational shaft 50a to clean the transparent window 26a and transparant window 26b. By the provision of the opening 51a, the cleaning blade deforms significantly adjacent the opening 51a, and the deformation of the other portion is not. The provision of the opening 51a is effective to decrease the rigidity of the cleaning blades 51. By changing the size, number and/or positions of the opening 51a, the rigidity of the cleaning blade and the contact angle between the edge of the cleaning blades 51 and the transparent window 26a or transparant window 26b can be properly selected as in embodiment 1. As a result, the same advantageous effects as in embodiment 1 can be provided even if the free length of the cleaning blade 51 is increased. Embodiment 3 Referring to Figure 13, a third embodiment of the present invention will be described As shown in Figure 13, a cleaning blade 56 having a partial narrow portion in place of the cleaning blade 51 of the foregoing embodiment. The narrowed portion is indicated by 56a. The structures of this embodiment are the same as embodiment 2 in the other respects. By the provision of the narrow portion 56a, the cleaning blade significantly deforms adjacent the narrow portion 56a, and the deformation of the other portion is not significant. The provision of the narrow portion 56a is also effective to decrease the rigidity of the cleaning blade 56. By changing the width, length and/or position of the narrow portion 56a, the rigidity of the cleaning blade and the contact angle between the edge of the cleaning blade 56 and the transparent window 26a or transparant window 26b can be properly selected as in embodiment 1. As a result, the same advantageous effects as in embodiment 1 can be provided even if the free length of the cleaning blade 56 is increased. Embodiment 4 Referring to Figure 14, the description will be made as to a fourth embodiment, wherein a cleaning blade 61 having a partially thin portion in place of the cleaning blades 51 in embodiment 2. The cleaning blade 61 mounted to an end 50b of the cleaning member 50 is provided with a thin portion 61a parallel with the rotational shaft 50a for the unshown cleaning member. The structures of this embodiment is the same as the second embodiment in the other respects. By the provision of a thin portion 61a, the cleaning blade deforms significantly t the a thin portion 61a, and the other portion does not. The provision of the a thin portion 61a, the rigidity of the cleaning blade 61 becomes small. By changing the width, thickness and/or position of the a thin portion 61a, the rigidity of the cleaning blade and the contact angle between the edge of the cleaning blade 61 and the transparent window 26a or transparant window 26b can be properly selected as in embodiment 1. As a result, the same advantageous effects as in embodiment 1 can be provided even if the free length of the cleaning blade 61 is increased. Embodiment 5 Referring to Figure 15, the description will be made as to a fifth embodiment (not covered by the present invention), wherein a cleaning blade 71 having a partial different material portion is used in place or the cleaning blades 51 in embodiment 2. The cleaning blade 71 mounted to an end 50b of the cleaning member 50 is provided with a portion of a material having a low rigidity at a base portion 71a of the cleaning blade. The interface between the different material portions is preferably extended substantially in parallel with the rotational shaft 50a. The other structures of this embodiment is the same as those of the embodiment 2. Because of the structure, the cleaning blade deforms significantly adjacent the base portion of the cleaning blade, and the deformation of the other portion is not significant. In addition, the rigidity of the cleaning blade 71 is small. By changing the material of the base portion of the cleaning blade, the rigidity of the cleaning blade and the contact angle between the edge of the cleaning blade 71 and the transparent window 26a or transparant window 26b can be properly selected as in embodiment 1. As a result, the same advantageous effects as in embodiment 1 can be provided even if the free length of the cleaning blade 71 is increased. The cleaning blade can be made by bonding of different materials or by two-color molding. Embodiment 6 Referring to Figures 16 and 17, the description will be made as to embodiment 6. Figures 16 and 17 are front view of the cleaning member of this embodiment and a longitudinal sectional view of a process cartridge of this embodiment, respectively. A cleaning blade 76 is fixed to a cleaning member 75 at an end 76b, and is supported by the end 75b of the cleaning member. The cleaning blade is provided with an opening 76a. The cleaning member 75 rotates by an unshown driving source about a shaft 75a in a direction F to clean the transparent window 26a and transparant window 26b. A stirring blade 77 feeds the developer T into a developing chamber through a mechanism as in embodiment 1. The structures of this embodiment is the same as in embodiment 1 in the other respects. By the provision of the opening 76a, the cleaning blade deforms significantly adjacent the opening 76a, and the deformation of the other portion is not significant . The provision of the opening 76a is effective to decrease the rigidity of the cleaning blade 76. By changing the configuration of the opening 76a, the rigidity of the cleaning blade and the contact angle between the edge of the cleaning blade 76 and the transparent window 26a or transparant window 26b can be properly selected as in embodiment 1. As a result, the same advantageous effects as in embodiment 1 can be provided even if the free length of the cleaning blade 76 is increased. In this embodiment, the fixed portion 76b of the cleaning blade 76 is located away from the edge of the cleaning blade beyond the rotational axis 75a of the cleaning member, with the result of longer free length. The fix position 76 b may be between the rotational axis of the cleaning member and the end of the cleaning blade or at the rotational center to the cleaning member. Similarly to embodiment 1, embodiments 2-6 satisfies the following: d(2m-d) (m-d) 2 = tan 2 N(2dm-d 2 ) 1/2 m(N-d) In Embodiments 1 - 6, the presence or absence of the developer T is detected by light transmission type sensor, but reflection type is usable wherein the presence or absence of the developer T is detected by a reflection type sensor in the process cartridge. In such a case, only one transparent window is provided, and the cleaning member 80 cleans only one window 26b. Embodiment 7 Referring to Figures 19 and 20, embodiment 7 will be described, wherein the toner scraping of the cleaning blade of this invention is used for developer feeding blade. Figure 19 is a sectional view of a process cartridge according to this embodiment, and Figure 20 is a perspective view of a stirring means which is a developer feeding means in this embodiment. Designated by 87 is a stirring blade, and is rotated in a direction G about a shaft 87a to feed the developer T into a developing chamber and to accomplish uniform distribution of the developer T. The bottom wall 85b of the developer container 85 is formed into a cylindrical shape with a center of the shaft 87a. A flexible blade 88 for feeding the developer T is mounted to the end 87b of the blade. With the rotation of the blade 87, the feeding blade 88 rotates while being in contact with the bottom wall 85 of the developer container to scrape the developer T deposited on the bottom wall 85b of the developer container and feed it to the developing chamber. The blade 88 is provided with a plurality of openings 88a at regular intervals in parallel with the shaft 87a of the stirring blade. The distance between the end of the feeding blade and the low rigidity portion is larger than m satisfying the following: d(2m-d) (m-d) 2 = tan 2 N(2dm-d 2 ) 1/2 m(N-d) where N is a free length of the feeding blade, and d is an entrance amount of the feeding blade into the bottom wall 85b of the developer container. According to this embodiment, even if the size of the blade 87 is reduced, the contact angle between the feeding blade and the developer container can be properly selected without the necessity of reducing the entrance amount d correspondingly at the proportional ratio. Therefore, the developer T can be fed to the developer chamber to the final end so that the process cartridge can be down sized while maintaining the conventional developer feeding performance.

Claims: A developing apparatus comprising: a developer container (25) for containing a developer; a light transmitting portion (26a, 26b), in said developer container (25), for optically detecting the developer; and a wiping sheet (28, 33, 51, 56, 61, 71, 76, 88) for wiping said light transmitting portion (26a, 26b); said wiping sheet (28, 33, 51, 56, 61, 71, 76, 88) being fixed on a rotatable cleaning member (29) along a line parallel to a rotational axis of said rotatable cleaning member, characterized in that said wiping sheet has a low rigidity portion provided by an opening or cut-away portion betwen the fixing position with said cleaning member and a distal edge of said wiping sheet. An apparatus according to Claim 1, wherein said wiping sheet has a narrow portion (56a) formed in said low rigidity portion. An apparatus according to Claim 1, wherein a distance M between the distal edge of said wiping sheet (28, 33, 51, 56, 61, 71, 76, 88) and the position of the low rigidity portion, a length N between the fixing position of said wiping sheet (28, 33, 51, 56, 61, 71, 76, 88) and the distal edge thereof, and an entrance amount d of said wiping sheet (28, 33, 51, 56, 61, 71, 76, 88) into the light transmitting portion (26a, 26b) satisfy: M>m, wherein m satisfies: d(2m-d) (m-d) 2 = tan 2 N(2dm-d 2 ) 1/2 m(N-d) An apparatus according to Claim 1, wherein the opening (28c, 33c, 51a, 76a, 88a) transmits light for developer detection. An image forming apparatus comprising: an image bearing member (21) for bearing an electrostatic image; a developing device (23) for developing the electrostatic image on said image bearing member (21), said developing device (23) including a developer container (25) for containing a developer; a light transmitting portion (26a, 26b) in said developer container (25), for optically detecting the developer; a wiping sheet (28, 33, 51, 56, 61, 71, 76, 88) for wiping said light transmitting portion (26a, 26b); said wiping sheet (28, 33, 51, 56, 61, 71, 76, 88) being fixed on a rotatable cleaning member (29) along a line parallel to a rotational axis of said rotatable cleaning member; an optical axis (R) for detecting the developer through said light transmitting portion (26a, 26b); and an optical element (15, 16) for detecting a developer through said light transmitting portion (26a, 26b), characterized in that said wiping sheet has a low rigidity portion provided by an opening or cut-away portion between the fixing position with said cleaning member and a distal edge of said wiping sheet. An apparatus according to Claim 5, wherein said developing device (23) is detachably mountable to a main assembly of said apparatus. An apparatus according to Claim 5, wherein said apparatus detects the presence or the absence of the developer on the basis of an output of said optical element (15, 16). An apparatus according to Claim 5, wherein said optical element (15) emits light toward the light transmitting portion (26a, 26b). An apparatus according to Claim 5, wherein said optical element (16) receives light from the light transmitting portion (26a, 26b). An apparatus according to Claim 6, wherein said developing device (23) is structurally connected with said image bearing member (21) to constitute a cartridge (20). An apparatus according to Claim 5, wherein said wiping sheet has a narrow portion (56a) formed in said low rigidity portion. An apparatus according to Claim 7, wherein a distance M between the distal edge of said wiping sheet (28, 33, 51, 56, 61, 71, 76, 88) and the position of the low rigidity portion, a length N between the fixing portion of said wiping sheet (28, 33, 51, 56, 61, 71, 76, 88) and the distal edge thereof, and an entrance amount d of said wiping sheet (28, 33, 51, 56, 61, 71, 76, 88) into the light transmitting portion (26a, 26b) satisfy: M>m, wherein m satisfies: d(2m-d) (m-d) 2 = tan 2 N(2dm-d 2 ) 1/2 m(N-d) An apparatus according to Claim 5, wherein the opening transmits light for developer detection.

Inventors: OSHIDA HARUHISA, OSHIDA, HARUHISA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1994
Main classification: G03G15
IPC codes: G03G15